Characterization of immunosuppressor cells in rats immunized with solubilized tumor-associated antigens prepared from a methylcholanthrene-induced fibrosarcoma.

Antiimmune responses in rats previously immunized with soluble tumor antigens prepared by sodium deoxycholate (DOC-STA) from chemically induced fibrosarcoma KMT-17 were measured by the Winn assay. Enhancement of tumor growth was demonstrated at a tumor:effector ratio of 1:500 with DOC-STA-immune spleen cells, although inhibition of tumor growth was demonstrated at a tumor:effector ratio of 1:100. The tumor-neutralizing ability of KMT-17-immune spleen cells was abrogated when DOC-STA-immune spleen cells were added to a mixture of KMT-17 cells and KMT-17-immune spleen cells. This suppressor activity of the spleen cells was diminished by the treatment with rabbit anti-rat T-cell serum and immune complement. The suppressor activity of DOC-STA-immune spleen cells was also shown in 51Cr release assay and was specific for the tumor line used. After fractionation of spleen cells from DOC-STA-immune rats by the Ficoll density gradient, the cells in the light layer showed an enhancing effect on tumor growth detected by the Winn assay, whereas the cells in the heavier region of the gradient had an inhibiting effect.